Membrane and Mitochondrial

It is contended that the renal slice technique measures primarily basolateral uptake of substrates or nephrotoxins, based on histological evidence of collapsed tubular lumens. This results in the inaccessibility of brush-border surfaces for reabsorptive transport (Burg and Orloff, 1969 Cohen and Kamm, 1976). This observation limits the ability of this model to accurately reflect reactions to nephrotoxins that occur as the result of brush-border accumulation of an injurious agent. Ultrastructurally, a number of alterations, particularly in the plasma membrane and mitochondrial compartments, have been shown to occur over a 2-h incubation period (Martel-Pelletier et al., 1977). This deterioration in morphology is very likely a consequence of the insufficient diffusion of oxygen, metabolic substrates, and waste products in the innermost regions of the kidney slice (Cohen and Kamm, 1976). Such factors also limit the use of slices in studying renal metabolism and transport functions. 

Ogbonme SM, Snhrbier A, Jones B, Cozzi SJ, Boyle GM, Morris M, McAlpine J, Johns TM, Scott KP, Sntherland JM, Gardner TTT, Le A, Lenarczyk D, Aylward JH, Parsons PG. (2004) Antitumor activity of 3-ingenyl angelate Plasma membrane and mitochondrial disruption and necrotic cell death. Cancer Res 64 2833-2839. 

Ultrastructural changes of proximal tubular cells occur as early as 1 hour after cephaloridine administration to rabbits and are characterized by loss of brush border, less elongated mitochondria and disappearance of structures associated with endocytosis. Later ultrastructural changes include disorganization of lateral interdigitations of plasma cell membrane and mitochondrial swelling [28,29]. 

Endopeptidase-24.16 (EC 3.4.24.16 neurolysin endopeptidase-24.16 neurotensin degrading endopeptidase oligopeptidase M) is zinc-metalloproteinase, found in soluble, membrane and mitochondrial forms. Notable substrates include angiotensin I, angiotensin II, bradykinin, neurotensin, substance P and somatostatin. Inhibitors include phosphorus-containing peptides, such as the dipeptide Pro-lie. 

The TRADD or FADD domains bind to adapter proteins in the cytosol and together they form of a death inducing signaling complex (DISC). This complex recruits caspase-8, one of a family of calcium ion-activated serine proteases (caspases) which cleave polypeptides on the C-terminal side of their aspartate residues. DISC activates caspase-8 to activate a Bcl-2 activator, BID (Fig. 13.1 Oa). The resultant tBid fragment activates effector Bcl-2 proteins on the endoplasmic reticular membrane and mitochondrial outer membrane. 

Liveanu, V., Webster, P. and Zilberstein, D. (1991). Localization of the plasma membrane and mitochondrial H -ATPases in Leishmania donovani promastigotes. Eur. J. Cell Biol. 54 95-101. 

Schackman RW, Christen R, Shapiro BM. 1984. Measurement of plasma membrane and mitochondrial potentials in sea urchin sperm. Changes upon activation and induction of the acrosome reaction. J Biol Chem 259 13914-13922. 

Interactions between fragments of a-synuclein and Afi peptide promote the aggregation of a-synuclein in vivo. In addition under pathlogical condition, interactions between Afi and a-synuclein may initiate the formation of toxic oligomers and nanopores that increase intracellular calcium leading to induction of oxidative stress, leakage of lysosomal membranes, and mitochondrial dysfunction (Crews et al., 2009). 

The PBRis distinct from the central BZ receptor although both can be present in the same tissues in differing ratios. PBRs are predominately localized on the outer mitochondrial membrane and are thus intracellular BZ recognition sites. The PBR is composed of three subunits an 18,000 mol wt subunit that binds isoquinoline carboxamide derivatives a 30,000 mol wt subunit that binds BZs and a 32,000 mol wt voltage-dependent anion channel subunit. The porphyrins may be endogenous ligands for the PBR. PBRs are involved in the control of cell proliferation and differentiation and steroidogenesis. 

Although the precise mechanism of the NADH-UQ reductase is not known, the first step involves binding of NADH to the enzyme on the matrix side of the inner mitochondrial membrane, and transfer of electrons from NADH to tightly bound FMN ... 

FIGURE 21.31 Structures of several uiicouplers, molecules that dissipate the proton gradient across the inner mitochondrial membrane and thereby destroy the tight coupling between electron transport and the ATP synthase reaction. 

The second electron shuttle system, called the malate-aspartate shuttle, is shown in Figure 21.34. Oxaloacetate is reduced in the cytosol, acquiring the electrons of NADH (which is oxidized to NAD ). Malate is transported across the inner membrane, where it is reoxidized by malate dehydrogenase, converting NAD to NADH in the matrix. This mitochondrial NADH readily enters the electron transport chain. The oxaloacetate produced in this reaction cannot cross the inner membrane and must be transaminated to form aspartate, which can be transported across the membrane to the cytosolic side. Transamination in the cytosol recycles aspartate back to oxaloacetate. In contrast to the glycerol phosphate shuttle, the malate-aspartate cycle is reversible, and it operates as shown in Figure 21.34 only if the NADH/NAD ratio in the cytosol is higher than the ratio in the matrix. Because this shuttle produces NADH in the matrix, the full 2.5 ATPs per NADH are recovered. 

FIGURE 24.9 The formation of acylcar-nitines and their transport across the inner mitochondrial membrane. The process involves the coordinated actions of carnitine acyltrans-ferases on both sides of the membrane and of a translocase that shuttles O-acylcarnitines across the membrane. 

Following the action of extraordinary stimulants (hypoxic hypoxia, hypoxia + hyperoxia, hypodynamia + hyperthermia), animals demonstrate an accumulation of malonic dialdehyde with a simultaneous fall of antiradical activity of the liver tissue. A preliminary introduction to rats of acetylene amine 3,4,5-tris(morpho-linopropynyl)-l-methylpyrazole 103 and also of tocopherol antioxidant and gutumine antihypoxant averts activation of the lipid peroxidation processes. The inhibition of peroxidation with this agent is mediated by stabilization of ly-zosomal and mitochondrial membranes. Unsaturated amines prevent destruction of the organelle membranes provoked by UV irradiation and incubation at 37°C (pH4.7)(78MIl). 

Long-chain fatty acids (e.g., palmitate Cig) diffuse through pores in the outer mitochondrial membrane, and then form long-chain acyl-CoA esters catalyzed reversibly by palmitoyl-CoA synthase (assumed to be on the inner face of the outer membrane). 

Figure 3. Mitochondrial fatty acid oxidation. Long-chain fatty acids are converted to their CoA-esters as described in the text, and their fatty-acyl-groups transferred to CoA in the matrix by the concerted action of CPT 1, the acylcarnitine/carnitine exchange carrier and CPT (A) as described in the text. Medium-chain and short-chain fatty acids (Cg or less) diffuse directly into the matrix where they are converted to their acyl-CoA esters by a acyl-CoA synthase. The mechanism of p-oxidation is shown below (B). Each cycle of P-oxidation removes -CH2-CH2- as an acetyl unit until the fatty acids are completely converted to acetyl-CoA. The enzymes catalyzing each stage of P-oxidation have different but overlapping specificities. In muscle mitochondria, most acetyl-CoA is oxidized to CO2 and H2O by the citrate cycle (Figure 4) some is converted to acylcamitine by carnitine acetyltransferase (associated with the inner face of the inner membrane) and exported from the matrix. Some acetyl-CoA (if in excess) is hydrolyzed to acetate and CoASH by acetyl-CoA hydrolase in the matrix. Enzymes ...

Another pathway is the L-glycerol 3-phosphate shuttle (Figure 11). Cytosolic dihydroxyacetone phosphate is reduced by NADFl to s.n-glycerol 3-phosphate, catalyzed by s,n-glycerol 3-phosphate dehydrogenase, and this is then oxidized by s,n-glycerol 3-phosphate ubiquinone oxidoreductase to dihydroxyacetone phosphate, which is a flavoprotein on the outer surface of the inner membrane. By this route electrons enter the respiratory chain.from cytosolic NADH at the level of complex III. Less well defined is the possibility that cytosolic NADH is oxidized by cytochrome bs reductase in the outer mitochondrial membrane and that electrons are transferred via cytochrome b5 in the endoplasmic reticulum to the respiratory chain at the level of cytochrome c (Fischer et al., 1985). 

While it has been known for many years that the N-terminal presequence is sufficient to promote mitochondrial targeting and assembly, the subsequent interaction of the precursor molecule with the outer mitochondrial membrane and the uptake of the protein is still an area of active research. There seems little doubt, however, that there are proteins on the outer mitochondrial membrane which are required for the import process. The function of these proteins is uncertain, but they may act as receptors with the subsequent transfer through the membrane at proteinous pores located at contact sites between the inner and outer membranes. Several proteins have been identified which seem to play an important role as either receptor proteins or part of the import channel (Pfanner et al., 1991). Again, not all proteins seem to depend on this mechanism. Cytochrome c, which is loosely associated with the outer aspect of the inner mitochondrial membrane, can cross... 

The steps in the subsequent utilization of muscle LCFAs may be summarized as follows. The free fatty acids, liberated from triglycerides by a neutral triglyceride lipase, are activated to form acyl CoAs by the mediation of LCFAcyl-CoA synthetase which is situated on the outer mitochondrial membrane. The next step involves carnitine palmitoyl transferase I (CPT I, see Figure 9) which is also located on the outer mitochondrial membrane and catalyzes the transfer of LCFAcyl residues from CoA to carnitine (y-trimethyl-amino-P-hydroxybutyrate). LCFAcyl... 

Henry, M.A., Nodes, E.E., Gao, D., Mazur, P., Critser. J.K. (1993). Cryopreservation of human spermatozoa. IV. The effects of cooling rate and warming rate on the maintenance of motility, plasma membrane integrity, and mitochondrial function. Fertil. and Steril. 60,911-918. 

Mechanistic studies have shown that TBT and certain other forms of trialkyltin have two distinct modes of toxic action in vertebrates. On the one hand they act as inhibitors of oxidative phosphorylation in mitochondria (Aldridge and Street 1964). Inhibition is associated with repression of ATP synthesis, disturbance of ion transport across the mitochondrial membrane, and swelling of the membrane. Oxidative phosphorylation is a vital process in animals and plants, and so trialkyltin compounds act as wide-ranging biocides. Another mode of action involves the inhibition of forms of cytochrome P450, which was referred to earlier in connection with metabolism. This has been demonstrated in mammals, aquatic invertebrates and fish (Morcillo et al. 2004, Oberdorster 2002). TBTO has been shown to inhibit P450 activity in cells from various tissues of mammals, including liver, kidney, and small intestine mucosa, both in vivo and in vitro (Rosenberg and Drummond 1983, Environmental Health Criteria 116). 

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